A camshaft adjusting device of said type is known from U.S. Pat. No. 6,450,137 B2. The device has an inner rotor which is screwed to the camshaft of the internal combustion engine by means of a central screw. The outer rotor is operatively connected to the crankshaft by means of a chain or a toothed belt. A relative rotary movement may be generated—controlled by means of an external hydraulic pressurization—between the inner rotor and the outer rotor. For this purpose, the inner rotor is embodied as a vane wheel which has grooves for holding vanes. The vanes separate a hydraulic chamber into two regions. An adjustment of the inner rotor relative to the outer rotor between an “early stop” and a “late stop” can be generated by means of corresponding pressurization of the respective section of the hydraulic chamber.
Thus, the camshaft adjuster has the function of varying the angular position of the camshaft with respect to the crankshaft of the internal combustion engine during operation. The angular position, which can be set with the described design, is stored in a characteristic map in an engine control unit and is defined substantially by the two parameters engine load and engine speed. During operation of the engine, the camshaft adjuster operates on the vane cell principle, that is to say the camshaft adjuster adjusts in the direction of the “early stop” or “late stop” by means of an oil pressure difference being generated in the hydraulic chambers.
During starting of the engine, there is the problem that there is insufficient oil pressure in the oil circuit of the engine in order to hold the camshaft adjuster in a certain position. As a result, the camshaft adjuster starts to oscillate in an uncontrolled manner. Furthermore, the striking of the vanes against the outer rotor (stator) generates noise.
It is known to solve the stated problem by providing axial locking between the inner rotor and a laterally arranged locking cover in the camshaft adjuster. Here, locking was usually provided in one of the end stop positions, “late” or “early”. Here, it is relatively easily possible for the locking play to be set before the assembly of the camshaft adjuster by means of corresponding positioning of the inner rotor with respect to the outer rotor. On the one hand, said play must not be too large, since otherwise undesired noise is generated; on the other hand, said play also must not be too small, since otherwise the locking pin (locking piston) can no longer lock or unlock reliably.
The locking in the end positions “early” and “late” however also has disadvantages, and it is therefore sought to be able to provide locking in a central position between “early” and “late”. “Center locking” differs from “end stop locking” in that the camshaft adjuster is locked in a defined angular position between the two end stops “early” and “late”, which is advantageous in particular during the starting of the internal combustion engine.
The above-cited U.S. Pat. No. 6,450,137 B2 makes this possible by means of two locking pins (locking pistons) which extend axially through the inner rotor. The locking pins can engage with their one axial end into two recesses which are formed into one of the side walls, which is designed as a locking cover, of the camshaft adjuster. The two locking pins are arranged parallel to one another and are spaced apart from one another radially.
A disadvantage of said design is that, on account of the tolerance chain of the components, that is to say specifically of the locking pins in their bores and the recesses in the locking cover, locking play is generated which—in contrast to that locking play which occurs with end stop locking—cannot be set before assembly.
The locking play is determined substantially by the geometric spacing between the two bores in the inner rotor for holding the locking pins and the spacing between the two locking recesses (locking guide slots) in the locking cover. The spacing is therefore determined significantly by the production tolerances, with no manipulation being possible during assembly in previously known solutions. The play of the locking pins in their holding bores in the inner rotor, the radial bearing play of the inner rotor in the outer rotor, the centering of the locking cover on the outer rotor, and the dimensional accuracy of the locking guide slot are also influential. All of these effects make it particularly difficult to maintain a defined locking play in a camshaft adjuster of the generic type.